Format in the Colombian 1st division:
For sponsorship reasons, the Colombian 1st division is currently [2017] called Liga Águila. There are 20 teams in the Colombian top flight, playing in 2 half-seasons each year, with two distinct champions, each coming out of an 8-team play-off round. The two half-seasons are called the Apertura [I] (played from ~early February to late May), and the Finalización [II] (played from ~early July to late November). The play-offs see large crowds in the 30-K range for many matches. Last year [2016], in regular-season matches, the Colombian 1st division averaged around 8.0 K per game, overall. There are about 8 teams in Colombia that can draw above 10-K or more, and the league is filled out with a dozen or so small clubs who draw in the 1-K-to-5-K-range. The 8 biggest clubs will be mentioned below, with crest and current kits shown. Then, further below near the foot of the post, all the small clubs who have won a title since 2000 will be briefly mentioned (4 clubs).

There can be wildly divergent crowd-sizes, year to year…the bigger Colombian clubs can draw very high one season, then have a massive drop in attendance the following year if the team does poorly – like up to seven or eight thousands-per-game drop-offs in crowd size. As for relegation/promotion, it is 2 teams-promoted and 2-teams-relegated per year, with the relegations based on a three-year average (like in Argentina). Just promoted for 2017 are the following two clubs: Colombian giants América de Cali (who have won 13 Colombian titles), and Tigres, a small club from a suburb of Bogotá called Soacha, who are making their top-flight debut in 2017, and who will be playing in a municipal-stadium-share with the another small club from the capial, La Equidad. There are two other stadium-shares in the league, currently. The other two Bogotá-based clubs, Millonarios and Santa Fe (the capital’s biggest two clubs), share the 36-K-capacity Estadio Nemesio Camacho (aka El Campín). Millonarios have been playing there since 1938; Santa Fe since 1952. And the two highest-drawing clubs in the country, Independiente Medellín and Atlético Nacional, both play at the 40-K-capacity Estadio Atanasio Girardot in Medellín, which opened in 1953.

Here is a very simplified history of the 1st division format in Colombia (1948 to 2017).
Although there have been 69 seasons of Colombian 1st Division football played [with 2017 to be the 70th season], there have been 84 Colombian 1st Division titles awarded (from 1948 to 2016).
-From 1948 to 1995, one title per season was awarded (1 title per year)…a February to December schedule (generally).
-Then a European-style schedule was tried (August to May), but that only lasted 2 seasons (in 1995-96 and in 1996-97).
-For the next 4 seasons – 1998 to 2001 – the format reverted back to the original 1 year/1 season format.
-Then in 2002, split seasons were introduced…with the Apertura (I) and Finalización (II) tournaments becoming separate, (two champions per year), but with the season containing both titles. A play-off is used to decide each split-season title (currently: 8-team play-off, with seeded head-to-head match-ups in a bracket-format).

Colombian 1st division: probably the 3rd-best in the Americas…
The Colombian 1st division is considered by most observers to be the third-best fútbol league in South America (or third-best in all the Americas for that matter) – after, of course, Argentina and Brazil {citation, IFFHS site from Jan. 2016}. Another indication of the relative strength of the Colombian 1st division can be seen by the fact that a Colombian club – Atlético Nacional – are the current champions of the most prestigious tournament in South America, the Copa Libertadores…

Atlético Nacional – the 2016 Copa Libertadores champions…
-From World Soccer.com, Tim Vickery’s Notes from South America: Reflections on Atletico Nacional’s Libertadores triumph (from 1 Aug. 2016 by Tim Vickery at worldsoccer.com).
-{My map-and-post for the 2017 Copa Libertadores, featuring an illustration for the 2016 Copa Libertadores champions, Atlético Nacional, here.}
Atlético Nacional beat Ecuador’s Independiente del Valle on 27 July 2016, 2-1 aggregate, for the club’s second Copa Libertadores title. (Atlético Nacional’s first Copa Liberadores title was won in 1989, when they defeated Paraguay’s Olimpia.) For the 2nd leg of the 2016 Finals, in Medellín, there was an overflow crowd of 46 K in the 40-K-capacity Estadio Atanasio Girardot. Atlético Nacional striker Miguel Borja scored in the 7th minute for the winner. Atlético Nacional are one of only two Colombian clubs to have won the Copa Libertadores. (The other Colombian club which has won a Copa Libertadores title is Once Caldas, in 2004/see Once Caldas section further below.)

Atlético Nacional were formed in 1947, one year before the pro era in Colombia began (in 1948). Atlético Nacional wear green-and-white. Their colors are derived from the flag of their home-region, Antioquia Department. Atlético Nacional are from Medellín, which has a metro-area-population of around 2.5 million, and is the 2nd-largest city in the country, after the capital, Bogotá. If you measure by ticket-paying fans, Medellín boasts the two biggest clubs in Colombia, one of which is Atlético Nacional, and the other being their main rival, Independiente (see next section, below). Both can very often draw above 25-K. Atlético Nacional, who draw in the 20K-to-29K-per-game range (most seasons), and who drew 27.9-K in 2016, are also the most-titled club in Colombia, having won the 1st-division title 15 times (last in 2015-II).

The two champions in the Colombian 1st division in 2016: Independiente Medellín and Santa Fe …Independiente Medellín won the Apertura-2016-I. Independiente wear red-jerseys-with-blue-pants. Independiente are one of the oldest clubs in Colombia, founded over three decades before the professional era there, in 1913. Their original kit featured black shirts, but the club have always sported a red-and-blue-shield device as their crest. At the club’s Spanish Wikipedia page, {here}, you can see Independiente’s original/1913-era crest, as well as a really nice version of the Independiente crest from the late 1990s (that turns the shape of the M in the badge into a symbolized-mountain-range). As mentioned, Independiente share a stadium with, and are the big local rivals of, the aforementioned Atlético Nacional. In terms of fanbase-size, it is hard to say which of the two is the bigger club, because like Atlético Nacional, Independiente also can draw in the mid-20K-to-low-30K-per-game range (and both clubs can definitely draw above 30-K come play-off time). En route to their Apertura title, Independiente ended up drawing highest in Colombia in 2016, at 28.2-K.

Santa Fe are from the capital, Bogotá (the largest city in the country, at around 8.0 million). Santa Fe won the Clausura-2016-II. Santa Fe wear Arsenal-style red-and-white, and sport a wonderfully minimalist crest (it is a simple blank-white-shield, with only their name and a small, red, off-center football on it). Santa Fe were formed in 1941, and 7 years later won the first pro title in Colombia in the inaugural 1948 season; they have won 9 titles (tied for fourth-most, with Deportivo Cali). Santa Fe, who draw between 9K-and-15K (most seasons), and drew 10.4-K in 2016, are not the biggest club in Bogotá – that would be their stadium-share-rivals Millonarios (see next paragraph). Santa Fe and Millonarios, as well as the aforementioned Atlético Nacional, are the only 3 clubs to never have been relegated and to have played every season of Colombian top flight football (70 seasons, including 2017).

Millonarios roots go back to the late 1930s, with a team formed in Bogotá by students of the Colegio San Bartolomé; they began being called Millonarios circa 1939, and the club was officially established in 1947. As their name suggests, Millonarios have historically had the larger share of middle-and-upper-class support amongst football fans in the capital, with Santa Fe having the larger share of working-class support in Bogotá. Millonarios wear blue-and-white, and are the second-most-titled club in Colombia, with 14 titles (last in 2012-II, but also with a recent long title-drought of 24 years, with no titles won between 1988 and 2014). Millonarios can draw between 14K-to-26K, and drew 15.0-K in 2016. And, like the two big Medellín teams, Millonarios can pull 30K+ when in the playoffs. Millonarios’ golden age was also the golden age of Colombian football, a time that has become known as the El Dorado – back in the early 1950s. {Here is an article-with-map that I posted in 2010: Colombia: Categoria Primera A, 2010 season, with a chart of the Colombian all-time champions list, from the professional era, spanning 1948 to 2009-II; and an overview of the El Dorado era (1949-1953).}

Rounding out the list of the 8-highest-drawing/8-most-successful Colombian clubs…América de Cali are from Cali (the 3rd-largest city in Colombia, at around 2.4 million). America de Cali are known as the Red Devils, and have just won promotion back to the 1st division. America can draw in the mid-20K-range when playing well (and they drew above 30K for their last home matches in late 2016, just before winning promotion). America have won the third-most Colombian titles, with 13 (last in 2008-II). Their best years also happened to coincide with the narco-trafficking era in Colombia (back in the mid-1990s to mid-2000s).

Junior are from up north on Colombia’s Caribbean coast, in Barranquilla (the nation’s 4th-largest city, at around 1.2 million). Being a port city, it was in Barranquilla that Colombian football most likely first began being played, about 110 years ago {see this from the Spanish Wikipedia, es.wikipedia.org/Primera A/Historia; translation: ”
It is not known for sure how soccer came to the country, although the first official match was played on March 6, 1908, an organized party and referee in the coastal city of Barranquilla.”}. Junior were formed in 1924, with the name Juventus (which is Latin for “Youth”) – the team was initially comprised mainly of Italian immigrants. By the early 1940s, the club’s name had morphed from Juventus to the Spanish term for youth, Juventude, then to the Anglicized version: Junior. Junior wear Atlético Madrid-style kits (red-and-white-stripes-atop-blue-pants). Junior draw pretty well…between 12K-and-20K (most seasons), and they drew third-best in the country last season, at 19.0-K. Junior have won the sixth-most Colombian titles, with 7 titles (last in 2011-II). Junior were runner-up in the Apertura-2016-I, losing out to Independiente.

Deportivo Cali are also from Cali (like America). Deportivo Cali are one of the oldest Colombian clubs (est. 1908; re-formed 1912), and wear green-and-white. They can draw in the 8K-to-12K range (most seasons), and drew 10.8-K in 2016. Deportivo Cali are one of the few Colombian clubs to own their own stadium, which opened in 2101. They play in the very large (too large, actually, at 52-K) Estadio Deportivo Cali, which is way out on the eastern edge of Greater Cali (in Palmira, which is 28 km/17 mi east of central Cali). Deportivo Cali are tied with Santa Fe for having won the fourth-most Colombian titles, 9 (last in 2015-I).

Once Caldas are from Manizales, which is not very large (it is the 19th-largest city in Colombia, with a population of around 370,000). Manizales is located within the triangle formed by Colombia’s 3 largest cities of Bogotá, Medellín, and Cali. Manizales is an important center of the coffee industry. Once Caldas usually draw around 8-to-9K, and can draw above 10-K in a good season (they drew 9.3-K in 2016). As it says at their Wikipedia page {here}, “The club was founded in 1961 after the fusion of Deportes Caldas and Deportivo Manizales (also known as Once Deportivo).” Once Caldas have won 4 Colombian titles (last in 2010-II). Once Caldas are known as El Blanco (the White), and sport a shield-crest that features the Italian flag. Once Caldas were shock winners of the 2004 Copa Libertadores, coming out of nowhere to beat Argentina’s Boca Juniors in the Finals by a score of 1-1 aggregate/2-0 penalties.

After that, the league roster is filled with about a dozen clubs which can only reach about 4-to-5-K per game in a good season.
But some of these smaller 1st division clubs can actually win titles, and the following 4 clubs all draw regularly below 5-K, yet have managed to win national titles in the 21st century…
-Deportes Tolima are from the 8th-largest city in Colombia, Ibagué (population of around .56 million). Tolima won the 2003-I title, and have been runner-up 6 times, including in the last campaign (in 2016-II, when they lost out to Santa Fe). Like Once Caldas in Manizales, Tolima is located within the triangle formed by Bogotá, Medellín, and Cali. Tolima wear dark-red-with-yellow; they drew 3.7-K in 2016.
-Deportivo Pasto are from Pasto (the 17th-largest city in the country, at about .45 million population). The city of Pasto is situated at the foot of a 1.5-mile-high volcano. Pasto are the southern-most and western-most top-flight club, located in the department of Nariño. Pasto won the 2006-I title. Like Tolima, Pasto also drew 3.7-K last season. They wear red-with-blue.
-Another small club that has won the title in relatively recent times is the currently-2nd-division side Boyacá Chicó, of Tunja (which is a pretty small city of only around 183,000). Boyacá Chicó were formed very recently, in Bogatá, in 2002, then won promotion to the top flight in 2003, then moved 130 km (80 mi) north-east to Tunja, in 2004, then won the 2008-I title. But after 13 seasons in the 1st division, Boyacá Chicó were relegated at the end of 2016.
-Another recent-title-winner currently stuck in the second division is Cúcuta Deportivo, who are from the 6th-largest city in Colombia, Cúcuta (population of around .64 million). Cúcuta Deportivo won the 2006-II title, but have been a bit of a yo-yo club since, and were relegated once again, in 2013.